Standard vs Non-standard Phraseology – differences between ICAO Level 4 and Level 6
The safety takeaway from the article is that Most aviation accidents are not caused by lack of English — but by lack of standard English and that:
If a message is important, it must be standard.
If it is not standard, it must be clear.
By all means, it is not about sounding professional — it is about being understood correctly, every time .
In this article, we would like to show you, though, that “Standard” is Not “Optional” and even if we use standard, there are differences between how we express ourselves, how we convey the messages and how clear they are for our listeners. The more advanced your language, the higher your ICAO LEVEL.
In an emergency, the human brain tends to revert to its native language or “plain English.” Training in ICAO phraseology creates muscle memory. By making the language “robotic,” aviation professionals ensure that even under extreme stress or oxygen deprivation (hypoxia), the communication remains functional and unambiguous .
Let’s look at the practical comparison examples between ICAO LEVEL 4 vs LEVEL 6.
1. ROUTINE SITUATION — TAXI CLEARANCE CONFUSION
Situation
The pilot is unsure about the assigned taxi route.
ICAO LEVEL 4
“Uh… we are not sure about the taxiway. Can you say again?”
Characteristics:
- Meaning is understandable
- Hesitation and filler words
- Limited precision
- Reactive, not proactive
- ☑ Operationally acceptable
- ❌ Not polished or safety-optimal
ICAO LEVEL 6
“Confirm taxi route to holding point runway two seven via Alpha.”
Characteristics:
- Clear and concise
- Correct structure
- No ambiguity
- Uses standard phraseology
- ☑ High situational awareness
- ☑ Professional and efficient
2. ABNORMAL SITUATION — WEATHER AVOIDANCE
Situation
Pilot needs deviation due to weather.
ICAO LEVEL 4
“We have weather ahead and need to go a little right.”
Characteristics:
- Message is clear
- Non-standard phrasing
- Vague distance and intent
- ☑ Message understood
- ❌ Limited detail
ICAO LEVEL 6
“Request ten degrees right for weather avoidance.”
Characteristics:
- Specific
- Standard ICAO structure
- Predictable phrasing
- ☑ Easier for ATC to respond
- ☑ Reduced misunderstanding
3. NON-STANDARD SITUATION — UNABLE CLEARANCE
Situation
Pilot cannot comply with altitude clearance.
ICAO LEVEL 4
“We cannot climb now because the aircraft is too heavy.”
Characteristics:
- Meaning clear
- Extra words
- Informal explanation
- ☑ Acceptable
- ❌ Inefficient
ICAO LEVEL 6
“Unable to climb due to aircraft performance.”
Characteristics:
- Short and standard
- Correct use of “unable”
- Professional register
- ☑ Ideal ICAO response
4. EMERGENCY-RELATED — TECHNICAL PROBLEM (NO MAYDAY)
Situation
Minor technical issue, no immediate danger.
ICAO LEVEL 4
“We have a small problem with the engine but it is okay.”
Characteristics:
- Vague
- Reassuring but unclear
- Poor information quality
- ❌ Risk of misunderstanding
ICAO LEVEL 6
“We have an engine indication abnormality, request to maintain present level.”
Characteristics:
- Precise
- Non-emotional
- Action-oriented
- ☑ Supports ATC decision-making
5. ACCIDENT / INCIDENT DISCUSSION (EXAM PICTURE TASK)
Situation
Candidate describes an aircraft damaged after runway excursion.
ICAO LEVEL 4
“The plane is damaged and it went out of the runway. Maybe the weather was bad.”
Characteristics:
- Basic description
- Limited vocabulary
- Simple speculation
- ☑ Minimum acceptable
ICAO LEVEL 6
“The aircraft appears to have overshot the runway after landing. The damage suggests a loss of directional control, possibly influenced by contaminated runway conditions.”
Characteristics:
- Accurate observation
- Controlled speculation
- Safety-focused language
- ☑ Examiner-level response
6. CRM / DECISION-MAKING QUESTION
Situation
Crew discussion after unstable approach.
ICAO LEVEL 4
“Why did you continue? It was not stable.”
Characteristics:
- Direct but confrontational
- Limited CRM tone
- ⚠ Understandable, but risky
ICAO LEVEL 6
“What factors influenced the decision to continue the approach?”
Characteristics:
- Neutral
- CRM-appropriate
- Encourages discussion
- ☑ Ideal for safety culture
7. KEY DIFFERENCES — QUICK EXAM SUMMARY
| Feature | ICAO Level 4 | ICAO Level 6 |
| Clarity | Adequate | Precise |
| Vocabulary | Limited | Aviation-specific |
| Structure | Basic | Predictable |
| Fluency | Some hesitation only | Natural & controlled |
| CRM tone | Neutral / direct | Professional & non-blaming |
| Safety impact | Acceptable | Optimal |
PART 2 — ADAPTATION FOR ATC
Now let’s reuse the same structure, but shift the perspective.
(Controller ↔ Pilot)
Key difference
- Pilots: compliance + clarification
- ATC: clarity, sequencing, anticipation
Pilot: “Request taxi.”
ICAO LEVEL 4 ATC:
“Taxi to runway two seven.”
⚠ Issues:
- missing holding point
- no taxi route
ICAO LEVEL 6 ATC:
“Taxi to holding point runway two seven via Alpha.”
☑ Complete ☑ Predictable ☑ Safe
ATC-SPECIFIC MARKING ADDITIONS
1. INFORMATION STRUCTURE (CRITICAL FOR ATC)
| Level | Examiner indicators |
| 4 | Correct but incomplete clearances |
| 6 | Complete, sequenced, unambiguous |
Listen for:
- runway number included
- route included
- restrictions included
2. ANTICIPATION & MONITORING
| Level | Examiner indicators |
| 4 | Reacts to pilot requests |
| 6 | Anticipates pilot needs |
Example:
- Level 6 ATC adds: “Expect further clearance at holding point.”
3. ERROR TRAPPING
| Level | Examiner indicators |
| 4 | Corrects errors when obvious |
| 6 | Detects incorrect readbacks immediately |
ATC INCIDENT DISCUSSION (for example PICTURE TASK)
ICAO Level 4
“The aircraft is damaged. Maybe it’s the pilot’s mistake.”
❌ Blame-focused
❌ Weak safety value
ICAO Level 6
“The image shows significant nose damage. Runway conditions and operational factors may have contributed.”
☑ System thinking
☑ Professional neutrality
ATC EXAMINER GOLDEN RULE A Level 6 controller does not just give clearances — they manage traffic through language.
Commonly Misunderstood Phrases in Aviation
Here is a breakdown of commonly misunderstood phrases, the risks they carry, and the ICAO Standard equivalents that keep the skies safe.
1. “Roger”
❌ Common misuse: “Roger” (used to mean yes / cleared / will do)
Risk:
- Does NOT mean compliance
- Has caused aircraft to enter runways or descend without clearance
ICAO Standard:
- Use “Wilco” → I understand and will comply
- Or full readback of the clearance
Example (safe): “Cleared to land runway two seven, ABC123.”
2. “Okay” / “Alright”
❌ Common misuse: “Okay, descending.”
Risk:
- Informal
- No legal meaning
- Can hide misunderstanding
ICAO Standard:
- Use “Descending”, “Climbing”, “Maintaining”
Example: “Descending to flight level one zero zero.”
3. “Takeoff” (used incorrectly)
❌ Common misuse: “Ready for takeoff.”
Risk:
- Correct only when actually clearing for takeoff.
- Runway incursions
- Fatal accidents (e.g. Tenerife)
ICAO Standard:
- Before clearance: “Ready for departure”
- Clearance: “Cleared for takeoff” (only ATC)
4. “At your discretion”
❌ Common misuse: “Descend at your discretion.” (without limits)
Risk:
- Different interpretations
- Uncontrolled descent profiles
ICAO Standard:
- Always include a limit
Example: “Descend at pilot’s discretion to flight level one eight zero.”
5. “As soon as possible”
❌ Common misuse: “Climb as soon as possible.”
Risk:
- Subjective timing
- Conflicting expectations between pilot and ATC
ICAO Standard:
- Use specific instructions
Example: “Climb now to flight level two four zero.”
6. “Continue” (Approach & Landing)
❌ Common misuse: “Continue.”
Risk:
- Pilot may interpret as landing clearance
- Contributed to approach and runway accidents
ICAO Standard:
- “Continue approach”
- “Cleared to land” only when appropriate
7. “Stand by”
❌ Common misuse: “Stand by.” (no follow-up)
Risk:
- Pilot waits indefinitely
- Critical time lost in abnormal situations
ICAO Standard:
- Use sparingly and re-contact quickly
- Or give conditional instruction
8. “We are good” / “No problem”
❌ Common misuse: “Everything is good now.”
Risk:
- Hides technical or operational issues
- ATC loses situational awareness
ICAO Standard:
- State status clearly
Example: “Technical issue resolved, able to continue.”
9. “Can you…?” instead of “Request…”
❌ Common misuse: “Can you give us lower?”
Risk:
- Sounds informal
- Weakens urgency
- Unclear operational intent
ICAO Standard:
- “Request lower altitude.”
10. “I think / maybe / probably”
❌ Common misuse: “I think we are on the wrong taxiway.”
Risk:
- Hesitation
- Delayed corrective action
ICAO Standard:
- “Confirm taxiway.”
- “We may be on incorrect taxiway.”
Summary Table (Training-Friendly)
| Non-Standard Phrase | Risk | ICAO-Standard Equivalent |
| Roger | No compliance | Wilco / readback |
| Okay | Informal | Descending / Climbing |
| Ready for takeoff | Runway incursion | Ready for departure |
| As soon as possible | Ambiguity | Climb now |
| Continue | Landing confusion | Continue approach |
| Can you… | Weak request | Request… |
| We’re good | Hidden risk | Status stated clearly |
For your information, please find more comparisons between level 4 and 6.
Task type: Routine / non-routine operational exchange
1. PRONUNCIATION
| Level | Examiner indicators |
| 4 | Accent noticeable but intelligible; occasional repetition required, misunderstandings occurred |
| 6 | Clear, natural pronunciation; no effort required to understand, no misunderstandings |
2. STRUCTURE & PHRASEOLOGY
The examiner listens for:
- correct verb use (request, confirm, unable)
- correct number format
- proper readbacks
| Level | Examiner indicators |
| 4 | Meaning clear, but wording sometimes non-standard, non-standard but acceptable |
| 6 | Consistent use of ICAO phraseology and correct structure, standard and precise |
3. FLUENCY
| Level | Examiner indicators |
| 4 | Some hesitation, fillers, reformulation, hesitation affects flow |
| 6 | Smooth delivery, appropriate pace, natural operational rhythm |
4. COMPREHENSION & INTERACTION
Key check: Does the candidate target missing information?
| Level | Examiner indicators |
| 4 | Responds correctly after clarification, vague clarification |
| 6 | Anticipates, clarifies proactively, precise clarification |
5. SAFETY IMPACT (Examiner Judgment)
Final examiner note: Does the candidate’s language support safe operations under pressure?
| Level | Examiner indicators |
| 4 | Communication adequate but not optimized |
| 6 | Communication actively reduces risk |
PICTURE DESCRIPTION / INCIDENT DISCUSSION
1. DESCRIPTION ACCURACY
| Level | Examiner indicators |
| 4 | Describes main elements, limited detail, observations mixed with assumptions |
| 6 | Accurate, structured, relevant details, observations clearly separated |
2. SPECULATION CONTROL
| Level | Examiner indicators |
| 4 | Uses “maybe”, “I think” frequently, uncontrolled speculation |
| 6 | Uses controlled phrases (appears to, suggests), professional speculation |
3. VOCABULARY RANGE
| Level | Examiner indicators |
| 4 | General aviation terms |
| 6 | Precise technical vocabulary |
4. CRM / SAFETY TONE
| Level | Examiner indicators |
| 4 | Neutral, sometimes direct, personal judgment language |
| 6 | Non-blaming, system-focused, safety-system language |
OVERALL ICAO DECISION SUPPORT
Examiner guidance:
- Level 4 = meaning achieved
- Level 6 = risk managed through language
Follow us for more differences between levels and requirements you must meet to reach level 5 or 6.
